Switch control module of switch mode power supply

Abstract

A switch control module for a switch mode power supply comprising a biased switch, an active switch and a control unit. The biased switch comprises a first node and a second node. The first node is coupled to a primary side winding. The active switch is connected to the second node. The control unit controls the ON/OFF states of the active switch and the biased switch is biased to be turned on initially. In this way, the active switch and the control unit are less likely to be damaged by voltage spikes generated by leakage in the primary side winding.

The invention claimed is: 
     
         1 . A switch control module, applied for a switch mode power supply, said switch power supply comprising a primary side winding and a secondary side winding, and said switch control module comprising:
 a biased switch, comprising a first node and a second node, and said first node coupled to said primary side winding;   an active switch, connected to said second node; and   a control unit, coupled to said active switch for controlling a switch state of said active switch;   wherein said biased switch is biased to a turn-on state, said biased switch further comprises a first switch unit; said biased switch is biased to turn on said first switch unit; when said control unit controls said active switch to turn off, the voltage at said second node will be raised to approaching a maximum voltage and turning off the said first switch unit.   
     
     
         2 . The switch control module of  claim 1 , wherein first switch unit is a metal-oxide-semiconductor field-effect transistor; the drain and source of said first switch unit act as said first node and said second node, respectively; the gate of said first switch unit receives a bias voltage; and the difference between said bias voltage and the threshold voltage of said first switch unit is said maximum voltage. 
     
     
         3 . The switch control module of  claim 1 , wherein said active switch comprises a second switch unit; and said control unit outputs a switch control signal to a control terminal of said second switch unit for controlling the turn-on or turn-off of said second switch unit. 
     
     
         4 . The switch control module of  claim 3 , wherein said active switch comprises a snubber coupled to said second node; and said snubber guides a spike absorption current to flow through said biased switch when said second switch unit is turned off by said control unit. 
     
     
         5 . The switch control module of  claim 4 , wherein said snubber comprises a current source and a third switch unit; and said current source and said third switch unit are connected in series for coupling to said second node. 
     
     
         6 . The switch control module of  claim 4 , wherein said control unit is coupled to said control terminal of said second switch unit via a third switch unit; said snubber comprises a first coupling device and a second coupling device; said first coupling device is coupled between said control unit and said control terminal of said second switch unit; and said second coupling device is coupled between said control terminal of said second switch unit and said second node. 
     
     
         7 . The switch control module of  claim 6 , wherein said second switch unit is turned on when said switch control signal is at a first level; said second switch unit is turned off when said switch control signal is at a second level; and said third switch unit is turned off when said switch control signal charge from said first level to said second level. 
     
     
         8 . The switch control module of  claim 3 , wherein said active switch comprises a fourth switch unit coupled between said second node and a power source terminal; and said power source terminal is coupled to a voltage stabilizing circuit for generating a direct-current power source using the voltage at said second node. 
     
     
         9 . The switch control module of  claim 8 , wherein said voltage stabilizing circuit comprises an output capacitor. 
     
     
         10 . The switch control module of  claim 8 , wherein said fourth switch unit is selectively turned on in a supply duration when said second switch unit is turned off. 
     
     
         11 . The switch control module of  claim 8 , wherein said power source terminal is coupled to said control unit for providing said direct-current power source to said control unit.